This invention relates to an intake air quantity control method for internal combustion engines, and more particularly to a method of this kind which is intended to mitigate a vacuum created in an intake passage downstream of a throttle valve therein, when the engine is decelerating, to thereby prevent lubricating oil loss, and also to stabilize engine idling rotation upon an increase in engine load.
In an internal combustion engine for automotive vehicles, when the engine is in certain conditions such as at deceleration, the engine is reversely driven by the driving wheels through the power transmission system, involving a problem that a high vacuum is created in the intake passage downstream of a throttle valve therein. This vacuum causes lubricating oil in an oil pan of the engine to be drawn up into the combustion chambers of cylinders, as well as causes lubricating oil in the valving system in the cylinder head to be drawn into the combustion chambers passing around valve stems mounted in the cylinder head, resulting in increased oil consumption. When the engine is in a warming-up condition, sliding portions of the engine have increased friction, and hence the engine rotation is unstable. Also, during idling the engine rotational speed is so low that an increase in engine load would render the engine rotation unstable.